The RNAs encoding two long fatty acid binding proteins (FABPs) are among the most abundant species which accumulate in the small intestinal lining cells (enterocytes) of rodents and man. These proteins (termed liver and intestinal FABP based on their initial sites of isolation) are members of a family of 8 small (14- 16 kDa) cytosolic polypeptides which bind hydrophobic ligands. Although their precise physiologic roles have not been defined, the two FABPs are most likely involved in the uptake, intracellular compartmentalization or metabolism of their ligands. We will use these FABPs as models to (i) define the molecular basis of fatty acid-protein interaction and (ii) identify cis acting elements which confer gastrointestinal specific gene expression. To achieve the first specific aim we will continue our crystallographic studies of rat intestinal FABP purified from E. coli containing a suitably constructed prokaryotic expression vector. Mapping studies will involve fusion of different portions of the 5' nontranscribed regions of the I and L-FABP genes to the human growth hormone structural gene, creation of transgenic mice and analysis of hGH gene expression in various murine tissues by RNA blot hybridization and immunocytochemical localization studies.